1. Field of the Invention
The present invention relates generally to improvements in suspension struts. More specifically, the invention relates to a valve that adjusts the dampening level of fluidic suspension struts to match the response of the strut to its level of steady-state loading.
2. Description of Related Art
Off-highway trucks are heavy duty, earth-moving vehicles that are typically used in mining operations or in other operations requiring the movement of large quantities of earth or other materials. Not surprisingly, the more efficiently these trucks move earth, the more profitable the operations. Many factors are taken into account to design these off-highway trucks for their intended use.
In a typical work cycle, an off-highway truck will position itself near a loading vehicle, such as a bucket loader or a power shovel. The loading vehicle fully loads the truck with material. The truck then hauls the material to a dumping site, which may be several miles away from the loading site. After the truck dumps the material at the dumping site, it returns to the loading site to pick up another load. It is clear that the efficiency of a truck increases as its cycle time decreases.
To increase efficiency, the speed, handling, and driver comfort of the truck must be improved. Off-highway dump trucks typically haul about 1.4 times their empty weight. Therefore, a truck with an empty weight of 350,000 lbs. would be capable of hauling about 240 tons of material. Off-highway trucks may be over 20 feet wide, 40 feet long, and 20 feet high. Although a vehicle of this size and weight is slow and handles poorly as compared with on-highway trucks, it is nonetheless important to maximize its speed and handling capabilities to minimize its cycle time.
Many factors limit the speed and handling capability of off-highway trucks. The suspension design is one of these factors. Typically, fluidic struts are used in the suspension system. These struts are typically filled with gas, which acts as a spring, and oil, which acts as a damper. Due to the enormous load carried by these struts, they must be highly charged to support the weight of a fully loaded truck. The dampening level of a typical strut is regulated by a fixed orifice that is sized as a compromise between the optimum size for an empty truck and the optimum size for a loaded truck. Therefore, when the truck is empty, its suspension tends to be overdamped resulting in a stiff ride and undesirable handling characteristics. This causes driver fatigue and increases the stress experienced by the truck's components, such as the frame, suspension and tires. When the truck is loaded, the suspension tends to be underdamped resulting in extensive low frequency loping. This also causes driver discomfort and results in reduced component life.
The present invention is directed to overcoming, or at least minimizing, one or more of the disadvantages set forth above.